Servo valves are used in a wide variety of industries to control the movement of hydraulic or pneumatic actuators in response to an input signal and are employed in industries where precise control of an actuator is required, for example in the aerospace industry. Servo valves alter the flow of a fluid through the valve in order to control the position, velocity, acceleration or force generated by an actuator, for example a hydraulic or pneumatic cylinder or motor.
A servo valve typically comprises a moving element (spool) and a fixed element. The relative movement of these two elements controls the flow of fluid through the valve.
A fluid manifold may be defined as any element which provides at least one flow path for fluids between one or more fluid inputs and one or more fluid outputs. As such, manifolds are found in many different applications. A typical servo valve manifold differs from manifolds in general in that it must accommodate a moveable spool within a cavity formed inside the manifold. As it is the position of the spool within the cavity which controls the fluid flow through the servo valve the internal dimensions of the manifold, and in particular of the cavity and the flow ports which open onto the cavity, must be produced to tight tolerances in order to achieve the necessary degree of precision in the control of the flow.
In contrast to the manifolds that may be found in other applications, size is commonly a key driver in servo valve design. For example, in aerospace applications the space and weight limitations within an aircraft may place severe constraints on the size of servo valve that can be accommodated.
A servo valve manifold may also include further cavities into which one or more flow management devices may be inserted. Flow management devices, for example check valves, flow restrictors and fluid filters act to alter the flow and ensure the smooth functioning of the fluid system of which the manifold forms a part.
Typically, servo valve manifolds are created by subtractive manufacturing processes. For example, a servo valve manifold may be created by removing material from a billet by machining. Alternatively, a servo valve manifold may be created by a combination of casting and subtractive manufacturing processes. For example the basic form of the manifold may be cast and the flow paths then created by removing material by machining (e.g. boring). Where greater precision is required a sleeve may be inserted within the manifold to isolate precision features from pressure and thermal distortions within the manifold and to enable the use of different materials, for example materials which have improved mechanical properties or are available at lower cost. Such manufacturing processes are relatively complex and involve a number of steps as well as a variety of different production techniques. These manufacturing processes also place limitations upon the type of manifold that can be produced. Consequently, it would be advantageous to provide an improved manufacturing process which is less complex and allows more flexibility in the design of servo valve manifolds. It would also be advantageous to provide an improved manifold which exploits the increased flexibility offered by such an improved manufacturing process.